A trial is not supposed to be an investigation. During a trial, lawyers only ask questions they already know the answer to. A trial is warranted only if the finished investigation gathered enough evidence that the likelihood of a murder conviction is very high.
I think a trial is warranted if the investigation shows a criminal act was committed and that conviction is reasonably high. If we only ever bothered trying to prosecute slam-dunk cases, we’d barely have any criminals in prison.
Also, I think that given what’s been released so far, a prosecution narrative of this being a well-meaning encounter handled poorly is a much easier sell and lends itself to manslaughter. Murder requires they prove ill intent going into the encounter. Manslaughter removes the burden of proving intent or mindset and looks simply at what took place.